1. Field of the Invention
The present invention relates to a thin film analyzing method useful for analyzing a specific component contained in a thin film comprising various components. More specifically, the invention relates to a thin film analyzing method useful for analyzing an effective component contained in an image recording layer of a planographic printing plate precursor, and which is capable of measuring, with high precision, the type, content, distribution and other factors of a component contained in the layer.
2. Description of the Related Art
Recent development in laser technology has progressed rapidly. In particular, solid lasers and semiconductor lasers having emission wavelengths within the range from near infrared ray wavelengths to infrared ray wavelengths, with both high-power and small size are readily available. These lasers are very useful for exposure light sources for recording materials, such as a planographic printing plate precursor, which is made from digital data in a computer or the like.
The recording material used in the recording layer of a positive planographic printing plate precursor for infrared ray lasers is a composition comprising, as essential components, a binder resin soluble in aqueous alkali solution, an infrared ray absorber (hereinafter referred to as “IR dye” as the case may be), which absorbs light to generate heat, and other components. When a coating, that is, a recording layer is formed on a support, the IR dye or the like in the recording layer interacts with the binder resin in a non-exposed portion (image portion), so as to function as a dissolution inhibitor for substantially lowering the solubility of the binder resin. Thus, the coating having resistance against development is maintained. In contrast, in an exposed portion (non-image portion), the interaction between the IR dye or the like and the binder resin is made weak by generated heat, so that the solubility of the binder resin in alkali developing solution is improved. Thus, after developing treatment, the non-image portion is removed and the maintained image portion is imagewise distributed. In this way, a planographic printing plate is formed.
However, in such a positive planographic printing plate material for development by infrared ray lasers, a difference between the resistance against solubility of the non-exposed portion (image portion) and the solubility of the exposed portion (non-image portion) is in-sufficient under various usage conditions. Thus, dependending on a variation in usage conditions, the following problems are easily caused: excessive development, that is, a film-decreasing phenomenon, which is generated by the dissolution of the coating in the image portion with the developing solution; poor development, that is, a film-remaining phenomenon, which is caused by failure of coating to be sufficiently dissolved and removed with the developing solution in the non-image portion; and other problems. In the case that a user's finger contacts the surface of the recording layer at the time of handling the plate material, thereby changing the surface state slightly, the non-exposed portion (image portion) is dissolved from the changed portion as a starting point at the time of developing the plate material. As a result, a scar state is generated so as to cause problems that the printing resistance deteriorates and the inking property becomes poor.
Such problems result from essential differences in plate-making mechanisms between positive planographic printing plate materials for infrared ray lasers and positive planographic printing plate materials made by UV exposure. In other words, positive planographic printing plate material made by UV exposure comprises, as essential components, a binder resin soluble in aqueous alkali solution, and an onium salt or quinone diazide compound. However, the onium salt or quinone diazide compound interacts with the binder resin in the non-exposed portion (image portion), to function as a dissolution inhibitor, and further in the exposed portion (non-image portion) the salt or compound is decomposed by light and gives an acid to function as a dissolution promoter. That is, the salt or compound has two functions.
In contrast, the IR dye or the like in the positive planographic printing plate material for infrared ray lasers functions only as a dissolution inhibitor for the non-image portion (image portion), and does not promote dissolution of the exposed portion (non-image portion). Therefore, in order to make the difference between the solubility of the non-exposed portion and that of the exposed portion evident in the positive planographic printing plate material for infrared ray lasers, it is necessary to use, as the binder resin therein, a resin having a high solubility in alkali developing solution. However, when such a binder resin is used, a problem of an unstable state before development is caused. If a binder resin having a low solubility in alkali developing solution is used to improve the strength of the image portion, the sensitivity is liable to be lowered or the film is liable to remain. Thus, the following serious problem is caused: the scope of developing-conditions for keeping the difference between the solubility of the image portion and that of the non-image portion (hereinafter referred to as development latitude) becomes narrow.
Various techniques have been developed to make the development latitude wide. For example, there is known a positive photosensitive image forming material comprising a resin which has a phenolic hydroxyl group and is soluble in aqueous alkali solution (for example, novolak resin), a substance which absorbs light to generate heat, and a positive photosensitive compound (for example, any one of various onium salts and quinine azide compounds) (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 7-285275). In such an image forming material, the positive photosensitive compound functions as a dissolution inhibitor for substantially lowing the solubility of the aqueous alkali solution soluble resin in the image portion, and in the non-image portion this compound does not exhibit dissolution inhibiting capability caused by heat, so that the compound is removed by development. As a result, an image is formed. In the case of such a positive image forming material, electrostatic interaction between the alkali soluble resin and the dissolution inhibitor is cancelled by heat generated from exposure, thereby improving the alkali solubility and removing the exposed portion by development, so as to form an image. This image forming material is characterized by using a thermally reversible reaction and small structural change of the material. Thus, it is feared that a sufficient dissolution promoting effect cannot be obtained and conversely various performances, such as processing stability and development latitude, are affected.
As described above, in the development of methods for providing preferable properties to planographic printing plate precursors, there are limitations in only investigating the mean for selecting components in the composition used in the image forming layer of the precursors. It has become necessary to investigate the physical properties of the inside of the image recording layer.
The present Applicant investigated this issue and then suggested a planographic printing plate precursor characterized in that the distribution of an infrared ray absorber and that of a colorant are different from each other in an image recording layer in order to improve the development latitude thereof. In such a case, it is important to accurately analyze correctly how the respective materials are distributed in the image recording layer which is a thin film.
Hitherto, various methods have been adopted in order to analyze the distribution of a material in a thin film along the depth direction thereof. For example, the step of using an ion gun or the like to sputter high energy beams to a coating and then subjecting the surface thereof to elementary analysis by X-ray photoelectron spectroscopy is repeated to analyze components, in the thin coating surface, which are not removed by the sputtering, whereby information about the thin coating along the depth direction thereof can be obtained. In this case, however, there is a high risk that materials in the thin coating are destroyed by the irradiation with the high energy beams from the ion gun or the like used in the sputtering. Thus, precise information cannot be easily obtained. In particular, when an organic compound present in the thin coating is detected, the compound is decomposed or evaporated by the irradiation with the high energy beams. Thus, precise measurement cannot be attained.
In recent years, a method has been suggested which comprises the steps of using a device called SAICAS (manufactured by DAIPLA WINTES Co., Ltd.) to cut a coating obliquely and then analyzing information along the depth direction by TOF-SIMS (see, for example, “63th, Applied Physics Scientific Lecture Meeting Proceedings” Lecture No. 27a-Q-5 (2002)). However, this device is originally a device for measuring exfoliating strength or shear strength. When this device is used to cut a coating obliquely to form an enlarged cross section, the following problems occur: (1) material of the cutting edge (knife) of the device is expensive diamond, and the cutting edge surface gets dirty with repeated usage of the cutting edge; (2) the cutting speed is very low (0.1 to 100 μm/sec), so that a long time is required for forming a sample; (3) when the device is applied to a planographic printing plate precursor, the tip of the cutting edge is damaged, which is minutely worked, because of high hardness of the support of the plate precursor, and the device is unsuitable for cutting the plate precursor from the surface of the coating to the support; and (4) the cut section is wavy and a flat and smooth cut face cannot be obtained.
As described above, many problems arise in analyzing a thin coating, particularly in analyzing information on a coating formed on a support along the depth direction thereof. Under the present circumstances, satisfactory results cannot be obtained according to conventional methods.